Printed wiring boards and their mounting frames of the character described, for example, in U.S. Pat. No. 4,002,381 of D. R. Wagner et al., issued Jan. 11, 1977, are well-known in the art and have long provided an advantageous means for assembling and mounting relatively large numbers of electrical components. Typically, circuits extending from the components in the form of wiring printed on the board are extended to terminal contact areas arranged along a leading edge of the board. These terminal areas are spaced to mate with corresponding contact springs of a connector into which the leading edge of the board is inserted. Suitable frames and racks are provided to support a number of the boards and also provide a means for guiding the boards for their insertion in and removal from the respective connectors. The connectors are in turn adapted to mate with pins extending from a backplane or with other interconnection apparatus as is also known. In order to achieve an orderly physical organization, the dimensions of the printed wiring boards are generally standardized within a given system and may even be so standardized among various suppliers. Although convenient from an interchangeability viewpoint, the fixed dimensions of a board within a given system and particularly the dimension of the board leading edge, ultimately imposes a severe limitation on the number of terminal contact areas which may be provided. This in turn limits the number of electrical components and circuits which may be mounted on the board notwithstanding the available board mounting area.
One obvious expedient in providing more board leading edge terminal contact areas is to decrease their widths and spacings; this measure, however, is temporary as minimum limits of the contact areas and spacings are approached. Additional columns of contact areas have in the past also been provided inwardly from the board leading edge, the resulting array of contact areas then being adapted to mate with multiple tiers of connector springs. Although significantly increasing the number of circuit board terminations, the latter arrangement presents a problem not encountered in connection with boards having a single leading edge column of terminal contact areas. When a single column board is inserted in its connector, each of its contact areas simultaneously makes electrical contact with its corresponding connector contact spring. No premature or erroneous electrical connections are normally possible during the time the board is being inserted. In a multicolumn contact arrangement, on the other hand, the connector contact springs adapted to make electrical connections with the contact areas of the circuit board beyond the first column of necessity pass each contact area of the preceding columns. Were the connector contact springs actually to wipe such preceding column board contact areas, serious damage could be done to board circuit components where the connector springs are included in active circuits. It is thus necessary in many system applications that the connector contact springs make simultaneous electrical contact with their respective circuit board terminal contact areas only at such time as the board is fully inserted in final opposition with the array of contact springs.
In one prior art interconnection arrangement, that disclosed in U.S. Pat. No. 4,018,495 of W. O. Freitag issued Apr. 19, 1977, a rider spring associated with the electrical contact spring prevents contact of the latter with a circuit board contact area until a predetermined point on the contact area is reached. The rider spring is adapted to slide along the board surface thereby maintaining the contact spring out of contact with the board contact area until a recess provided in the board surface receives the rider spring. At that time, the electrical connection is completed. Only a single electrical connection is thus made at a predetermined point in the relative movement of the circuit board and contact spring. It is thus the problem of achieving selective and simultaneous contact of an array of circuit board contact areas and a corresponding array of contact springs to which the apparatus of this invention is chiefly directed.